First, are you absolutely sure that the ball is the wrong one? (You probably are, but you might as well be absolutely certain.) And are both the bladder and the shell undersize, or just one?
Check in with FIRST at
frcteams@usfirst.org, to make them aware of the issue. They might be able to add it to your missing parts request, as a courtesy, and if anyone knows where to buy the balls, it's them.
Also, if you know of any other teams in the area, consider asking them to borrow the ball for testing. (FIRST's website has teams listed by geographic region, if you need more information.)